This invention relates generally to filtering of motorcycle engine lubricating oil; and more particularly concerns a highly advantageous filter unit employed in series with the engine oil circulation system.
Filters employed in the past for filtering engine crankcase oil have included pressure relief devices that require a relatively large 0-ring to move readily and stretch on a conical surface to uncover a relief port; however, the 0-ring is subject to malfunction, and sediment can clog and cake at interstices between the ring and cone. These difficulties are enhanced due to the fact that the 0-ring is normally at a high level, above the main extent of the filter, and thus not lubricated by oil standing in a tank that receives the filter; also, the 0-ring and cone decrease substantially the overall filtering length of the filter unit, so that the unit needs more frequent replacement than would be the case if the 0-ring and conical wall were not used. There is need for an improved filter that avoids these difficulties.